Essay on Endothelium in Health and Disease

902 WordsDec 24, 20124 Pages
Investigation of the influence of the endothelium on the actions of acetylcholine and nitroprusside. Results (a) Estimate the maximum responses (Emax) and EC50 values for phenylephrine with the two types of arterial ring. Put this data in a single, self-explanatory table. Table1. Emax and EC50 values for phenylephrine. Phenylephrine | Emax in grams tension | EC50 in nM | Endothelium intact | 2.2 | 40 | Endothelium denuded | 2.9 | 10 | (c) Estimate the EC50 values for the effects of acetylcholine and nitroprusside in both types of arterial ring, and present these in a table. Table 2. EC50 values for the effect of acetylcholine and nitroprusside. EC50 in nM |…show more content…
Shearing forces acting on the vascular endothelium generated by blood flow causes a release of calcium and subsequent cNOS (cyclic nitric oxide synthase) activation. Therefore, increases in blood flow stimulate NO formation (flow-dependent NO formation). Nitric oxide then causes independent vasodilation by inhibiting vasoconstrictor influences of phenylephrine and alters its potency and contractile effect. (Richard E. Klabunde. 2010) However, it has a short half-life of only a few seconds. In endothelial denuded preparations there was no production of nitric oxide and subsequently no flow dependent vasodilation occurred. So, without endothelium a response of phenylephrine is not inhibited and therefore it exhibits a higher potency(lower EC50) and efficacy. f) Account for the response to acetylcholine in the two preparations. Which receptor(s) mediates the effects of acetylcholine in the rings with and without endothelium? As shown in the table 2 the EC50 values of acetylcholine, calculated from the dose-response curve, significantly differ from each other. In fact, in endothelium denuded rings acetylcholine caused no relaxation at all. Moreover, the prolonged exposure to increasing concentrations had given some constriction. In human and animals 5 sub types of muscarinic receptors (M1-M5) have been identified. In the particular case of human blood vessels, the M3 subtype seems to be prevalent on endothelial cells as
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